Undo CL16853912 now that CL16922241 fixes the deadlock properly.

#rb none

[CL 16926361 by Zousar Shaker in ue5-main branch]

Engine/Source/Developer/TextureCompressor/Private/TextureCompressorModule.cpp

@@ -2133,7 +2133,7 @@ static bool CompressMipChain(
 				Work.DestMip
 			);
 		}
-	}, EParallelForFlags::Unbalanced | EParallelForFlags::BackgroundPriority);
+	}, EParallelForFlags::Unbalanced);
 
 	for (int32 TaskIndex = 0; TaskIndex < AsyncCompressionTasks.Num(); ++TaskIndex)
 	{